A monocular night vision system basically incorporates a single eyepiece lens assembly, image intensifier assembly, and objective lens assembly. Most monocular night vision devices (MNVDs) are compact and lightweight to optimize hand-held use. MNVDS are often referred to as pocket scopes since they could optimally be small enough to be stored in a user's pockets.
Numerous MNVDs exist in the prior art. Examples of some of these night vision devices, including hand-held night vision devices, include U.S. patent application Ser. No. 08/108,989 entitled NIGHT VISION MONOCULARS, filed Aug. 18, 1993; U.S. patent application Ser. No. 08/405,172 entitled COMPACT NIGHT VISION DEVICE, filed Mar. 16, 1995; U.S. Pat. No. 5,644,425, issued Jul. 1, 1997, entitled NIGHT VISION MONOCULAR WITH UNISTRUCTURAL OPTICAL BED also teaches a hand-held night vision device for use in both military and non-military applications, however these devices generally suffer from a combination of poor performance characteristics and design shortcomings which lead to inefficient device operation or limited flexibility, and poor performance. For example, a number of the monocular night vision devices have main housings which are made of metallic material which make them rugged, but heavy. Moreover, prior art MNVDs are often bulky and uncomfortable to hold in one's hand and are difficult to operate when deployed in completely dark areas. Furthermore, prior art MNVDs are often energy efficient, expending battery power even when not in use, such as during daylight. In the event of a headmounted device, prior art MNVDs did not automatically turn off when removed from the helmet mount or when flipped up in the helmet mount. Still further, prior art devices could not be mounted to an M16/M4 receiver rail configured for the Modular Weapon System Kit (which fits the mounting rail defined in MIL-STD-93), and standard AN/PVS-7 accessories such as the lens cap, sacrificial filter, compass, 3X magnifier, and light interference filter could not be attached to the objective lens assembly of these devices.
As one can ascertain, night vision systems frequently need to include some control functions beyond just "on" and "off". Users commonly want additional features such as: a low-battery indicator, an infrared illuminator for use in very dark areas, an indicator that the infrared illuminator is activated, an automatic cut-off in high-light conditions, an automatic cut-off when the viewing device is flipped up to a stowed position or removed from its mount, and a variable gain control. These features can be implemented piecemeal, or as parts of an integrated control system.
The prior art AN/PVS-7 night vision device, manufactured by IT Corporation, the assignee herein, represents an integrated control system device. The AN/PVS-7 is a binocular viewer having one objective lens, one image intensifier tube, and two eyepieces which view the same output image from the tube via an arrangement of a beam splitter and turning mirrors. The AN/PVS-7 is intended predominantly for use by military ground forces, and can be hand-held or attached to a head mount or helmet mount.
The AN/PVS-7 includes a control circuit which is an application-specific integrated circuit (ASIC), implemented in a complementary metal-oxide semiconductor (CMOS) process, and including both digital and analog subcircuits. This ASIC includes a high-light cutoff circuit described in commonly assigned U.S. Pat. No. 4,843,29, entitled HIGH LIGHT LEVEL CUTOFF APPARATUS FOR USE WITH NIGHT VISION DEVICE, issued to J. Reed and J. Caserta, and incorporated herein by reference. FIG. 6 shows the prior art circuit illustrated in the above patent (FIG. 2 of U.S. Pat. No. 4,843,229) where most of the functional blocks shown are contained in the ASIC. Only the light sensor 8, the crystal 22, the voltage multiplier 4, the power field-effect transistor (FET) 3, the battery 1, the goggles (intensifier tube) 2, and the on/off switch are not located inside the ASIC, due to their unsuitability for implementation in the CMOS process. The crystal 22 may be replaced by a resistor-capacitor (RC) timing network, in order to reduce cost while still providing sufficient timing accuracy. This ASIC also includes circuitry to implement a flashing low-battery indicator and flip-up cutoff. In the AN/PVS-7, the ASIC and its associated electronic parts, including the voltage multiplier 4, the power FET 3, RC timing network, and some associated power filtering components are assembled on one small surface-mount rigid printed circuit board or ceramic substrate. Other parts, including the on/off/ir switch, the connections for the intensifier tube, the light sensor (photo resistor or photo transistor), the infrared illuminator, the low battery indicator light-emitting diode (LED), the infrared indicator LED, and the magnetic reed switch (which is the sensor for the flip-up cutoff function) are required to be located elsewhere in the overall housing, due to physical access or optical exposure requirements. These parts are interconnected to the main circuit via a flexible polyamide circuit with etched copper conductors. The battery contacts are connected by wires to the rest of the circuit.
The flip-up cutoff feature assures that the user does not inadvertently leave the viewing device on or give away his position by exposing the glow from the intensifier, when the viewing device is removed from its mount or is flipped up to the stowed position. The flip-up cutoff feature functions as follows. The magnetic reed switch is placed in the AN/PVS-7 viewing device housing, inside the housing wall which is in proximity to the mounting point. The magnetic reed switch is a single-pole, double-throw device. In the de-energized (no magnetic field applied) state, the magnetic reed switch connects an input of the ASIC to the positive supply voltage considered logic "high". In the energized (magnetic field applied) state, the magnetic reed switch connects the input of the ASIC to the negative supply voltage. This is considered logic "low". A small magnet is placed in the head mount and helmet mount, in a location proximal to the mounting point for the viewing device. When the viewing device is installed in the mount, the magnetic reed switch comes in proximity to the magnet, the reed switch is energized, and the ASIC input transits from a logic high state to a logic low state, provided the viewing device has been turned on. The ASIC contains logic which ignores the reed switch state at the moment when the viewing device is turned on, and also ignores high-to-low transitions of the input from the reed switch. Thus, the viewing device can be switched on whether or not it is in the mount, and the viewing device will not turn off when it is installed in the mount. When the viewing device is removed from the mount or flipped up to the stowed position in the mount, the magnetic reed switch is separated from proximity to the magnet. The reed switch is thus de-energized, and the ASIC input transits from a logic low state to a logic high state, (provided the viewing device has been turned on). The transition from low to high is interpreted by the logic in the ASIC as a command to turn the intensifier off, causing the latching flip-flop 7 to close, grounding the gate electrode of the power FET 3. The power FET 3 ceases to conduct, turning off the intensifier and turning off the infrared illuminator and indicator, if on. Once the ASIC turns the intensifier off, the user must switch the viewing off and back on to restore the operation of the intensifier.
The low battery indicator provides a visual warning to the user that the battery is in need of replacement, prior to the time when the intensifier would fail due to lack of sufficient operating voltage. The low battery indicator circuit in the ASIC makes use of the voltage reference 10 and an additional comparator like the comparator 9. The battery voltage is fed through a voltage divider resistor pair in the ASIC to an input of the additional comparator. The other input of the comparator is fed by the voltage reference 10. When the divided battery voltage falls below the level of the reference voltage, the comparator causes intermediate outputs from the counter 20 to be combined to form a pulsing current waveform that flashes the low battery indicator LED. The flashes from the LED are visible through a small hole in the turning mirror associated with the eyepiece for the user's right eye. The tap at the junction of the divider resistor pair in the ASIC is connected to an input of the ASIC. This input makes is possible to adjust the voltage threshold at which the low battery indicator begins to flash. The tap of a divider resistor pair or potentiometer external to the ASIC is connected to the ASIC input. Trimming either of the divider resistors or adjusting the potentiometer changes the voltage threshold, and enables the threshold to be precisely set to the desired value regardless of manufacturing variations in the ASIC.
The infrared (ir) illuminator enables the user to illuminate a very dark area with infrared illumination which the image intensifier can "see", but which is invisible to the human eye. The illuminator comprises an infrared emitter diode which is mounted in an aperture in the AN/PVS-7 housing, and is aimed forward to illuminate the field of view of the intensifier. In addition to the illuminator a visible LED serves as an infrared indicator to warn the user that the infrared illuminator is in use. In similar fashion to the low battery indicator LED, the infrared indicator LED is visible through a small hole in the turning mirror associated with the eyepiece for a user's eye. The infrared illuminator and infrared indicator are switched on via the third position on the off/on/ir switch. The user can activate ir momentarily by rotating the switch knob to the ir position, or can activate ir continuously by pulling and rotating the switch knob to the ir position. The ir position on the switch applies battery power to the ir illuminator, ir indicator, as well as to the intensifier and associated circuits. The power returns for the ir illuminator, ir indicator, and intensifier are through the power switching FET 3 so that the high light cutoff and flip-up cutoff circuits can deactivate these functions.
However, a number of problems associated with prior art night vision devices currently exist. Such problems include the lack of a variable gain feature, and a night vision device operable in a small, lightweight package, such as a monocular. The monocular enables the user to keep one eye dark-adapted for a wide-field view, while using the monocular with the other eye to see specific details, even in shaded areas. The variable gain feature allows the user to maintain partial dark-adaptation, if desired, in the eye using the intensifier, and allows the user to defeat the automatic brightness control function in the intensifier, which some users find to be annoying. The reduced size and weight of a monocular, as compared to a binocular, improves the maneuverability of the user, and reduces fatigue. The flexibility of the monocular to be mounted to a rifle, as well as to be mounted to the head or helmet and used with either eye, as well as to be used hand-held, expands its utility for the user.
Further, in systems which have interchangeable tubes and variable gain, it is preferable that any tube be capable of installation in any system and yet retain the same maximum and minimum gain limits, with no adjustment of limits required. The ability to replace or interchange tubes without requiring gain limit adjustments means that maintainers can do their work faster and with less support equipment, reducing maintenance costs.
The monocular device according to the present invention eliminates the size and weight associated with the mounting adapter, output optical splitter, image erector, and mirrors associated with the bi-ocular viewer. In addition, this monocular capitalizes on the small size and light weight of the MX-10160 image intensifier tube, as compared to the larger MX-10130 tube used in the AN/PVS-7 system. The monocular features are described in more detail in a commonly assigned related patent application, entitled IMPROVED MONOCULAR NIGHT VISION DEVICE, and incorporated herein by reference. The MX-10160 tube is modified to include the ability for the user to adjust the intensifier's gain to any desired value between specified upper and lower limits, which can be factory-preset. The factory-preset tubes are interchangeable in monoculars, without requiring the maintainers to adjust the preset gain settings. The variable gain tube is described in more detail in a related patent application, entitled VARIABLE GAIN IMAGE INTENSIFIER, and also incorporated by reference.
According to the present invention, a novel electronic circuit to be used in conjunction with the monocular makes use of the items previously developed for the AN/PVS-7, and adds provisions for variable gain, without requiring the maintainers to adjust the monocular circuit when replacing the intensifier tube. In addition, the novel circuit achieves reduced size and improved producibility by including all functions, except for the switches, batteries, and gain control, on one rigid printed circuit board (pcb). The switches, batteries, and gain control are interconnected by a single flexible pcb which interconnects to the rigid pcb. This approach eliminates hand wiring, enables simplified, quicker assembly, and improves reliability by eliminating wire joints which can be prone to flexural fatigue failure or short circuits caused by loose strands.
To reduce size and weight of the monocular, the head/helmet mount adapter is made part of a detachable mounting arm. Such a feature imposes additional requirements on the circuit, as the magnetic reed switch does not reside in the main housing, but is now in a detachable mounting arm. The circuit includes features for enabling the detachment while protecting from damage and preventing inadvertent turn-off during the periods when the mounting arm is detached. In this invention, components and features are added to the flip-up cutoff circuit to harmlessly absorb any electrostatic discharges (esd) to the contacts and to prevent unintended turn-off events. In the present invention, the flip-up cutoff circuit contacts on the monocular housing are recessed slightly below the mounting surface to protect the contacts from mechanical damage and to prevent electrical contact to a small arms mounting adapter, which does not include a flip-up cutoff function. Further, the number of connections to the reed switch is reduced from three to two, and new filtering provisions have been added to prevent magnetic reed switch bounce from causing unintended turn-off events.